Dissolution of a feldspathic lherzolite and its implications on geologic carbon storage

Storage of carbon dioxide as thermodynamically stable carbonate minerals has been proposed for control of atmospheric carbon dioxide levels. CO2 storage by mineralization, however, requires that the (i) pH of CO2-rich water increases to the pKa2 of the carbonate system and (ii) kinetic constraints on nucleation of carbonates (e.g. magnesite) or hydrocarbonates are overcome before carbonate minerals are precipitated. Therefore, enhanced weathering and carbonate alkalinity production may provide a more plausible method for neutralization of CO2 because it eliminates the need for items (i) and (ii). In this context, ultramafic formations with significant hydraulic conductivity such as that of feldspathic lherzolite deposits should be considered as potential host formation. In this study, we reacted a coarse-grained feldspathic lherzolite from Tamarack, MN with Milli-Q water equilibrated with atmospheric CO2 levels to observe its dissolution characteristics and the rate at which pH approaches pKa1 of the carbonate system at ambient pressure and temperature, hence producing carbonate alkalinity.